import cv2
from matplotlib import pyplot as plt

img = cv2.imread('dog.jpg', 0)
# 全局阈值化
ret1, th1 = cv2.threshold(img, 127, 255, cv2.THRESH_BINARY)
# Otsu's thresholding
ret2, th2 = cv2.threshold(img, 0, 255, cv2.THRESH_BINARY + cv2.THRESH_OTSU)
# 高斯滤波后的阈值化
# （5,5）为高斯核的大小，0 为标准差
blur = cv2.GaussianBlur(img, (5, 5), 0)
ret3, th3 = cv2.threshold(blur, 0, 255, cv2.THRESH_BINARY + cv2.THRESH_OTSU)
# 绘制所有图像及其直方图
images = [img, 0, th1, img, 0, th2, blur, 0, th3]
titles = ['Original Noisy Image', 'Histogram', 'Global Thresholding (v=127)',
          'Original Noisy Image', 'Histogram', "Otsu's Thresholding",
          'Gaussian filtered Image', 'Histogram',
          "Otsu's Thresholding"]

# 这里使用了 pyplot 中画直方图的方法，plt.hist, 要注意的是它的参数是一维数组
# 所以这里使用了（numpy）ravel 方法，将多维数组转换成一维，也可以使用 flatten 方法
# ndarray.flat 1-D iterator over an array.
# ndarray.flatten 1-D array copy of the elements of an array in row-major order.
for i in range(3):
    plt.subplot(3, 3, i * 3 + 1), plt.imshow(images[i * 3], 'gray')
plt.title(titles[i * 3]), plt.xticks([]), plt.yticks([])
plt.subplot(3, 3, i * 3 + 2), plt.hist(images[i * 3].ravel(), 256)
plt.title(titles[i * 3 + 1]), plt.xticks([]), plt.yticks([])
plt.subplot(3, 3, i * 3 + 3), plt.imshow(images[i * 3 + 2], 'gray')
plt.title(titles[i * 3 + 2]), plt.xticks([]), plt.yticks([])
plt.show()